Apparatus and method for performing foreign object detection in wireless power transfer system

ABSTRACT

Provided are an apparatus and method for performing foreign object detection in a wireless power transfer system. The present specification discloses a method comprising receiving a digital ping from the wireless power transmitter; transmitting an identification and configuration packets to the wireless power transmitter; transmitting a foreign object detection (FOD) state packet which indicates a reference Q factor of the wireless power receiver to the wireless power transmitter; and receiving wireless power through magnetic coupling from the wireless power transmitter based on the foreign object detection result of the wireless power transmitter using the reference Q factor. Irrespective of individual characteristics of a wireless power receiver, accuracy and reliability of detecting a foreign object may be improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/217,170, filed on Mar. 30, 2021, which is a continuation of U.S.patent application Ser. No. 16/915,836, filed on Jun. 29, 2020, now U.S.Pat. No. 10,971,955, which is a continuation of U.S. patent applicationSer. No. 16/375,823, filed on Apr. 4, 2019, now U.S. Pat. No.11,050,300, which claims the benefit of earlier filing date and right ofpriority to Korean Patent Application No. 10-2018-0045256, filed on Apr.18, 2018, the contents of which are all hereby incorporated by referenceherein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless power transfer system and,more particularly, to an apparatus and method for performing foreignobject detection in a wireless power transfer system.

Related Art

Wireless power transfer is a technology for transferring electricalpower wirelessly between a power source and an electronic device. In oneexample, wireless power transfer technology allows the battery of awireless terminal such as a smartphone or table to be charged simply byputting the terminal on a wireless charging pad, thereby providingexcellent mobility, convenience, and safety compared with the existingcharging environment using wired charging connectors. Wireless powertransfer technology is getting attention as a means to replace theexisting wired power transfer environment in various fields such asconsumer electronics, industrial machines, military devices,automobiles, infrastructure, and medical devices.

The Wireless Power Consortium (WPC), which is leading standardization ofthe wireless power transfer technology, has classified electronicdevices into a few groups according to the amount of transmitted andreceived power and is developing standards for the respective groups.For example, a first group is developing a small power standard (lessthan about 5 W or about 30 W) aimed for wearable devices including asmart watch, smart glass, Head Mounted Display (HMD), and smart ring;and mobile electronic devices (or portable electronic devices) such asan earphone, remote controller, smartphone, PDA, and tablet PC. A secondgroup is developing a mid-power standard (less than about 60 W or about200 W) aimed for mid-sized/small-sized home appliances such asnotebooks, robot cleaners, TVs, sound devices, vacuum cleaners, andmonitors. A third group is developing a large power standard (less thanabout 2 kW or 22 kW) aimed for kitchen appliances such as a blender,microwave oven, and electric rice cooker; and personal mobility devices(or electronic devices/mobility means) such as a wheelchair, electrickickboard, electric bicycle, and electric car.

In the terminal supply system, as long as a charger and a device areconnected properly, there is little possibility that an impeding factorsuch as a foreign object interfering with charging of the device liesbetween them. On the other hand, due to the nature of contactlesscharging, a wireless power transfer system may allow an unnecessaryforeign object to lie between a wireless power receiver and a wirelesspower transmitter during charging. When a foreign object such as metalexists between a wireless power transmitter and a wireless powerreceiver, not only power transfer is not carried out smoothly due to theforeign object but also a problem such as overload or fire damage andexplosion of a product due to the foreign object may occur. To solve theproblem, various methods for detecting a foreign object have beenintroduced, but the foreign object may not be detected properly becauseof differences in the characteristics of individual wireless powerreceivers. Therefore, an apparatus and method for improving accuracy andreliability of detecting a foreign object irrespective of individualcharacteristics of a wireless power receiver are required.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus and methodfor improving reliability and accuracy of detecting a foreign object ina wireless power transfer system.

Another object of the present invention is to provide an optimal Qfactor which guarantees reliable detection of a foreign object in awireless power transfer system.

Yet another object of the present invention is to provide an apparatusand method for performing detection of a foreign object based on theoptimal Q factor in a wireless power transfer system.

According to one aspect of the present invention, a method for receivingwireless power from a wireless power transmitter by a wireless powerreceiver based on detection of a foreign object in a wireless powertransfer system is provided. The method comprises receiving a digitalping from the wireless power transmitter; transmitting an identificationand configuration packets to the wireless power transmitter;transmitting a foreign object detection state packet which indicates areference Q factor (Q_(ref)) of the wireless power receiver to thewireless power transmitter; and receiving wireless power throughmagnetic coupling from the wireless power transmitter based on theforeign object detection result of the wireless power transmitter usingthe reference Q factor.

Here, the reference Q factor is a Q factor of a reference wireless powertransmitter with respect to the wireless power receiver in the absenceof a nearby foreign object, wherein the reference Q factor may be largerthan or equal to the minimum reference Q factor (Q_(ref_min)) requiredfor an arbitrary wireless power receiver compatible with the referencewireless power transmitter.

In one aspect, provided that a first Q factor (Q_(RX)) of a referencewireless power transmitter with respect to the arbitrary wireless powerreceiver in the absence of a nearby foreign object is the same as asecond Q factor (Q_(RX,RFO)) of the reference wireless power transmitterwith respect to the arbitrary wireless power receiver in the presence ofa nearby representative foreign object (RFO), if the first Q factor isdenoted as a threshold Q factor (Q_(ref,OX)) by which the representativeforeign object may be detected, the minimum Q factor value may bedefined based on the threshold Q factor.

In another aspect, when ΔQ factor=second Q factor−first Q factor, theminimum reference Q factor may be defined based on the first Q factorwhich satisfies ΔQ factor=0; the first Q factor may be a Q factor of areference wireless power transmitter with respect to the arbitrarywireless power receiver in the absence of a nearby foreign object; andthe second Q factor may be a Q factor of the reference wireless powertransmitter with respect to the arbitrary wireless power receiver in thepresence of a nearby representative foreign object.

In yet another aspect, the minimum reference Q factor may be defined asa value compensating the threshold Q factor for a Q factor measurementerror.

In still another aspect, the threshold Q factor may range from 22 to 23,the Q factor measurement error may lie within 10% of the threshold Qfactor, and the minimum reference Q factor may range from 24 to 26.

In still yet another aspect, the threshold Q factor may be 22.2.

In a still further aspect, the minimum reference Q factor may range from24.7 to 25.

In a still additional aspect, the representative foreign object may be arepresentative foreign object which maximizes the threshold Q factoramong various types of representative foreign objects.

According to another aspect of the present invention, a method fortransferring wireless power to a wireless power receiver by a wirelesspower transmitter based on detection of a foreign object in a wirelesspower transfer system is provided. The method comprises transmitting adigital ping to the wireless power receiver; receiving an identificationand configuration packets from the wireless power receiver; receiving aforeign object detection state packet which indicates a reference Qfactor (Q_(ref)) of the wireless power receiver from the wireless powerreceiver; performing foreign object detection by using the reference Qfactor; and transferring wireless power through magnetic coupling to thewireless power receiver based on the foreign object detection result.

Here, the reference Q factor is a Q factor of a reference wireless powertransmitter with respect to the wireless power receiver in the absenceof a nearby foreign object, wherein the reference Q factor may be largerthan or equal to the minimum reference Q factor (Q_(ref_min)) requiredfor an arbitrary wireless power receiver compatible with the referencewireless power transmitter.

In one aspect, provided that a first Q factor (Q_(RX)) of a referencewireless power transmitter with respect to the arbitrary wireless powerreceiver in the absence of a nearby foreign object is the same as asecond Q factor (Q_(RX,RFO)) of the reference wireless power transmitterwith respect to the arbitrary wireless power receiver in the presence ofa nearby representative foreign object (RFO), if the first Q factor isdenoted as a threshold Q factor (Q_(ref,OX)) by which the representativeforeign object may be detected, the minimum Q factor value may bedefined based on the threshold Q factor.

In another aspect, when ΔQ factor=second Q factor−first Q factor, theminimum reference Q factor may be defined based on the first Q factorwhich satisfies ΔQ factor=0; the first Q factor may be a Q factor of areference wireless power transmitter with respect to the arbitrarywireless power receiver in the absence of a nearby foreign object; andthe second Q factor may be a Q factor of the reference wireless powertransmitter with respect to the arbitrary wireless power receiver in thepresence of a nearby representative foreign object.

In yet another aspect, the minimum reference Q factor may be defined asa value compensating the threshold Q factor for a Q factor measurementerror.

In still another aspect, the threshold Q factor may range from 22 to 23,the Q factor measurement error may lie within 10% of the threshold Qfactor, and the minimum reference Q factor may range from 24 to 26.

In still yet another aspect, the threshold Q factor may be 22.2.

According to yet another aspect of the present invention, a method fortesting foreign object detection performance of a wireless powerreceiver in a wireless power transfer system is provided. The methodcomprises measuring a Q factor with respect to a wireless power receiverat a predetermined test position on a reference wireless powertransmitter; comparing the measured Q factor with a reference Q factorprovided by the wireless power receiver; and if the reference Q factoris larger than or equal to the minimum reference Q factor (Q_(ref_min))required for an arbitrary wireless power receiver compatible with thereference wireless power transmitter, and the measured Q factor belongsto an error range of the reference Q factor, determining a foreignobject detection performance test of the wireless power receiver asbeing successful.

In one aspect, provided that a first Q factor (Q_(RX)) of a referencewireless power transmitter with respect to the arbitrary wireless powerreceiver in the absence of a nearby foreign object is the same as asecond Q factor (Q_(RX,RFO)) of the reference wireless power transmitterwith respect to the arbitrary wireless power receiver in the presence ofa nearby representative foreign object (RFO), if the first Q factor isdenoted as a threshold Q factor (Q_(ref,OX)) by which the representativeforeign object may be detected, the minimum Q factor value may bedefined based on the threshold Q factor.

In another aspect, when ΔQ factor=second Q factor−first Q factor, theminimum reference Q factor may be defined based on the first Q factorwhich satisfies ΔQ factor=0; the first Q factor may be a Q factor of areference wireless power transmitter with respect to the arbitrarywireless power receiver in the absence of a nearby foreign object; andthe second Q factor may be a Q factor of the reference wireless powertransmitter with respect to the arbitrary wireless power receiver in thepresence of a nearby representative foreign object.

In yet another aspect, the minimum reference Q factor may be defined asa value compensating the threshold Q factor for a Q factor measurementerror.

In still another aspect, the threshold Q factor may range from 22 to 23,the Q factor measurement error may lie within 10% of the threshold Qfactor, and the minimum reference Q factor may range from 24 to 26.

In still yet another aspect, the threshold Q factor may be 22.2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a wireless power system 10according to one embodiment of the present invention.

FIG. 2 illustrates a block diagram of a wireless power system 10according to another embodiment of the present invention.

FIG. 3 illustrates an embodiment of various electronic devices to whicha wireless power transfer system is applied.

FIG. 4 illustrates a block diagram of a wireless power transfer systemaccording to another embodiment of the present invention.

FIG. 5 is a state transition diagram illustrating a wireless powertransfer procedure.

FIG. 6 illustrates a power control method according to one embodiment ofthe present invention.

FIG. 7 illustrates a block diagram of a wireless power transmitteraccording to another embodiment of the present invention.

FIG. 8 illustrates a wireless power receiver according to anotherembodiment of the present invention.

FIG. 9 illustrates a communication frame structure according to oneembodiment of the present invention.

FIG. 10 illustrates a structure of a sync pattern according to oneembodiment of the present invention.

FIG. 11 illustrates operation states of a wireless power transmitter andwireless power receiver in a shared mode according to one embodiment ofthe present invention.

FIG. 12 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter used for an experiment of thepresent embodiment.

FIG. 13 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter; and four representative foreignobjects used for an experiment of the present embodiment.

FIG. 14 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter; and a secondary coil, shieldingunit, and metal case member of a reference wireless power receiver usedfor an experiment of the present embodiment.

FIG. 15 illustrates a simulation result according to the embodiment ofFIG. 14.

FIG. 16 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter; a secondary coil, shielding unit,and metal case member of a reference wireless power receiver; andrepresentative foreign objects used for an experiment of the presentembodiment.

FIGS. 17a to 17d illustrate a simulation result performed in theenvironment of FIG. 16 according to the present embodiment.

FIG. 18 illustrates a flow diagram of a method for receiving wirelesspower from a wireless power transmitter based on foreign objectdetection by a wireless power receiver according to one embodiment ofthe present invention.

FIG. 19 illustrates a flow diagram of a method for transmitting wirelesspower to a wireless power receiver based on foreign object detection bya wireless power transmitter according to one embodiment of the presentinvention.

FIG. 20 illustrates a flow diagram of a method for testing foreignobject detection performance of a wireless power receiver in a wirelesspower transfer system according to one embodiment of the presentinvention.

FIG. 21 is a block diagram of an FOD state packet according to oneembodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The term “wireless power” used in what follows refers to an energy in anarbitrary form related to an electric, magnetic, or electromagneticfield transferred to a wireless power receiver from a wireless powertransmitter without involving physical electromagnetic conductors.Wireless power may also be called a wireless power signal and indicatean oscillating magnetic flux enclosed by a primary and secondary coils.For example, power transform in a system for charging devices includingmobile phones, cordless phones, iPods, MP3 players, and headsets may bedescribed in this document. In general, basic operating principles ofwireless power transfer include, for example, a method for transferringpower through magnetic coupling, method for transferring power throughradio frequency (RF), method for transferring power through microwaves,and method for transferring power through ultrasonic waves.

FIG. 1 illustrates a block diagram of a wireless power system 10according to one embodiment of the present invention.

Referring to FIG. 1, a wireless power system 10 comprises a wirelesspower transmitter 100 and a wireless power receiver 200.

The wireless power transmitter 100 receives power from an external powersource S and generates a magnetic field. The wireless power receiver 200receives power wirelessly by generating a current from the generatedmagnetic field.

Also, in the wireless power system 10, the wireless power transmitter100 and wireless power receiver 200 may transmit and receive variousinformation required for wireless power transfer. Here, communicationbetween the wireless power transmitter 100 and wireless power receiver200 may be performed by using either in-band communication usingmagnetic fields used for wireless power transfer or out-bandcommunication using a separate communication carrier.

Here, the wireless power transmitter 100 may be provided as a fixed ormobile type apparatus. Fixed-type examples include transmitters embeddedin the indoor ceiling or wall or furniture such as a table; transmittersinstalled in the form of an implant in an outdoor parking area, busstation, or subway station; and those installed in a transportationmeans such as a vehicle or train. A mobile type wireless powertransmitter 100 may be implemented as part of another apparatus such asa mobile apparatus having a portable weight and size or cover of anotebook computer.

The wireless power receiver 200 has to be interpreted as a comprehensiveconcept including various types of electronic devices equipped withbatteries and various types of home appliances which receive operatingpower wirelessly instead of through a power cable. Typical examples ofthe wireless power receiver 200 include a portable terminal, cellularphone, smartphone, Personal Digital Assistant (PDA), Portable MediaPlayer (PMP), Wibro terminal, tablet, pablet, notebook, digital camera,navigation terminal, television, and electric vehicle (EV).

The wireless power system 100 may include one or more wireless powerreceivers 200. Although FIG. 1 illustrates a situation in which awireless power transmitter 100 and wireless power receiver 200 give andtake power in a one-to-one fashion to and from each other, it is alsopossible that one wireless power transmitter 100 transfers power to aplurality of wireless power receivers 200-1, 200-2, . . . 200-M as shownin FIG. 2. In particular, if wireless power transfer is performedthrough magnetic resonance, one wireless power transmitter 100 maytransfer power to multiple wireless power receivers 200-1, 200-2, . . ., 200-M simultaneously by employing a simultaneous transmission methodor time division transmission method.

Also, although FIG. 1 illustrates a situation in which a wireless powertransmitter 100 transmits power directly to a wireless power receiver200, a separate wireless power transceiver such as a relay or repeatermeant for increasing a wireless power transfer distance may be usedbetween the wireless power transmitter 100 and the wireless powerreceiver 200. In this case, power may be transmitted from the wirelesspower transmitter 100 to a wireless power transceiver, and the wirelesspower transceiver may again transmit power to the wireless powerreceiver 200.

In what follows, a wireless power receiver, power receiver, and receiverrefer to the wireless power receiver 200. Also, a wireless powertransmitter, power transmitter, and transmitter mentioned in the presentspecification all refer to the wireless power transmitter 100.

FIG. 3 illustrates an embodiment of various electronic devices to whicha wireless power transfer system is applied.

FIG. 3 shows and classifies electronic devices according to the amountof transmitted and received power to and from a wireless power transfersystem. Referring to FIG. 3, a small power (less than about 5 W or 30 W)wireless charging method may be applied to wearable devices such as asmart watch, smart glass, Head Mounted Display (HMD), smart ring; andmobile electronic devices (or portable electronic devices) such as anearphone, remote controller, smartphone, PDA, and table PC.

A mid-power (less than about 50 W or 200 W) wireless charging method maybe applied to middle/small home appliances such as a notebook, robotcleaner, TV, sound equipment, vacuum cleaner, and monitor. A large power(less than about 2 kW or 22 kW) wireless charging method may be appliedto kitchen appliances such as a blender, microwave oven, and electricrice cooker; and personal mobility devices (or electronicdevice/mobility means) such as a wheelchair, electric kickboard,electric bicycle, and electric vehicle.

The aforementioned (or shown in FIG. 1) electronic devices/mobilitymeans may each include a wireless power receiver to be described later.Therefore, the aforementioned electronic devices/mobility means may becharged by receiving power wirelessly from a wireless power transmitter.

In what follows, descriptions are given with respect to a mobile deviceto which a wireless power transfer system is applied; however, thedescriptions given below are only an embodiment, and a wireless chargingmethod according to the present invention may be applied to variouselectronic devices described above.

Wireless power transmitters and receivers may provide a very convenientuser experience and interface (UX/UI). In other words, a smart wirelesscharging service may be provided. A smart wireless charging service maybe implemented based on the UX/UI of a smartphone equipped with awireless power transmitter. To support the application, an interfacebetween a processor of the smartphone and a wireless power receiverallows “drop and play” bilateral communication between a wireless powertransmitter and receiver.

As one example, a user may experience a smart wireless charging servicein a hotel. When the user enters a hotel room and put his or hersmartphone on a wireless charger inside the room, the wireless chargertransmits wireless power to the smartphone, and the smartphone receivesthe wireless power. During this process, the wireless charger transmitsinformation about the smart wireless charging service to the smartphone.If the smartphone detects being put on a wireless charger, detectsreception of wireless power, or receives information about a smartwireless charging service from the wireless charger, the smartphoneenters a state in which the smartphone inquires of the user aboutwhether to opt in to an additional feature. To this purpose, thesmartphone may display a message on the screen with or without an alarmsound. An example of the message may include a sentence such as “Welcometo ### hotel. Select “Yes” to activate smart charging functions: Yes|NoThanks.”. The smartphone receives a user input which selects Yes or NoThanks and performs the next procedure selected by the user. If Yes isselected, the smartphone transmits the corresponding information to thewireless charger. And the smartphone and wireless charger performs asmart charging function in conjunction with each other.

The smart wireless charging service may also include receivingauto-filled WiFi credentials. For example, a wireless charger transmitsa WiFi credential to the smartphone, and the smartphone automaticallyenters the WiFi credential received from the wireless charger byexecuting an appropriate application.

The smart wireless charging service may also execute a hotel applicationproviding a hotel promotion or obtain remote check-in/check-out andcontact information.

As another example, the user may experience a smart wireless chargingservice inside a car. If the user gets in a car and puts his or hersmartphone on a wireless charger, the wireless charger transmitswireless power to the smartphone, and the smartphone receives wirelesspower. During the procedure, the wireless charger transmits informationabout the smart wireless charging service to the smartphone. If thesmartphone detects being put on a wireless charger, detects reception ofwireless power, or receives information about a smart wireless chargingservice from the wireless charger, the smartphone enters a state inwhich the smartphone inquires identity of the user.

In this state, the smartphone is automatically connected through WiFiand/or Bluetooth. The smartphone may display a message on the screenwith or without an alarm sound. An example of the message may include asentence such as “Welcome to your car. Select “Yes” to synch device within-car controls: Yes|No Thanks.”. The smartphone receives a user inputwhich selects Yes or No Thanks and performs the next procedure selectedby the user. If Yes is selected, the smartphone transmits thecorresponding information to the wireless charger. And by activatingin-car application/display software, the smartphone and wireless chargermay perform an in-car smart control function in conjunction with eachother. The user may enjoy desired music and check a normal map position.The in-car application/display software may include a function whichprovides synchronization access for passengers.

As yet another example, the user may experience smart wireless chargingat home. If the user goes into a room and puts his or her smartphone ona wireless charger, the wireless charger transmits wireless power to thesmartphone, and the smartphone receives wireless power. During theprocedure, the wireless charger transmits information about the smartwireless charging service to the smartphone. If the smartphone detectsbeing put on a wireless charger, detects reception of wireless power, orreceives information about a smart wireless charging service from thewireless charger, the smartphone enters a state in which the smartphoneinquires of the user about whether to opt in to an additional feature.To this purpose, the smartphone may display a message on the screen withor without an alarm sound. An example of the message may include asentence such as “Hi xxx. Would you like to activate night mode andsecure the building?. Yes|No Thanks.”. The smartphone receives a userinput which selects Yes or No Thanks and performs the next procedureselected by the user. If Yes is selected, the smartphone transmits thecorresponding information to the wireless charger. The smartphone andwireless charger may at least recognize a pattern of the user and advisethe user to close a door or window, turn off the light, or set thealarm.

The standard for wireless power transmission includes standardsdeveloped by the Wireless Power Consortium (WPC), Air Fuel Alliance(AFA), and Power Matters Alliance (PMA)

The WPC standard defines a baseline power profile (BPP) and extendedpower profile (EPP). BPP pertains to a wireless power transmitter andreceiver supporting power transmission of 5 W, and EPP pertains to awireless power transmitter and receiver supporting power transmissionranging from 5 W to 30 W.

Various wireless power transmitters and receivers using different powerlevels may be covered by the respective standards and may be classifiedinto different power classes or categories.

For example, the WPC classifies wireless power transmitters andreceivers into power class (PC)-1, PC0, PC1, and PC2; and provides astandard document for each PC. The PC-1 standard is related to awireless power transmitter and receiver providing guaranteed power lessthan 5 W. Applications of the PC-1 class include wearable devices suchas a smart watch.

The PC0 standard is related to a wireless power transmitter and receiverproviding guaranteed power of 5 W. The PC0 standard includes EPP, theguaranteed power of which reaches up to 30 W. Although in-band (IB)communication is a mandatory communication protocol of the PC0 standard,out-of-band (OOB) communication which is used as an optional backupchannel may also be employed. A wireless power receiver may checkwhether OOB is supported by setting an OBB flag within a configurationpacket. A wireless power transmitter supporting OOB may enter an OOBhandover phase by transmitting a bit-pattern for OOB handover as aresponse to the configuration packet. The response to the configurationpacket may be NAK, ND, or newly defined 8-bit pattern. Applications ofthe PC0 include smartphones.

The PC1 standard is related to a wireless power transmitter and receiverproviding guaranteed power ranging from 30 W to 150 W. OOB communicationis a mandatory communication channel for PC1, and IB communication isused for initialization to the OOB communication and link establishment.A wireless power transmitter may enter an OOB handover phase bytransmitting a bit-pattern for OOB handover as a response to aconfiguration packet. Applications of the PC1 include laptops or powertools.

The PC2 standard is related to a wireless power transmitter and receiverproviding guaranteed power ranging from 200 W to 2 kW, and itsapplications include kitchen appliances.

As described above, the PC may be distinguished according to the powerlevel, and whether to support compatibility between the same PCs may bedetermined as optional or mandatory. Here, compatibility between thesame PCs indicates that power transmission and reception are possiblebetween the same PCs. For example, when a wireless power transmitter ofPC x is capable of charging a wireless power receiver of the same PC x,it may be regarded that compatibility between the same PCs ismaintained. Similarly, compatibility between different PCs may also besupported. Here, compatibility between different PCs indicates thatpower transmission and reception is allowed between different PCs. Forexample, when a wireless power transmitter of PC x is capable ofcharging a wireless power receiver of PC y, it may be regarded thatcompatibility between different PCs is maintained.

Support of compatibility between PCs is a very important issue in termsof user experience and infrastructure construction. However, it shouldbe noted that maintaining compatibility between PCs raises varioustechnical problems as described below.

In the case of compatibility between the same PCs, for example, awireless power receiver based on a laptop charging scheme where chargingmay be performed reliably only when power is transmitted continuouslymay run into a problem in receiving power reliably from a powertool-based wireless power transmitter which transmits powerintermittently, even if the power tool-based wireless power transmitteris of the same PC. Also, in the case of compatibility between differentPCs, for example, if a wireless power transmitter of which the minimumguaranteed power is 200 W transmits power to a wireless power receiverof which the maximum guaranteed power is 5 W, the wireless powerreceiver may be damaged from overvoltage. As a result, it is difficultto use PC as an indicator/criterion representing/indicatingcompatibility.

In what follows, ‘profile’ will be newly defined as anindicator/criterion representing/indicating compatibility. In otherwords, between wireless power transmitter and receiver having the same‘profile’, compatibility is maintained, and reliable power transmissionand reception is allowed while power transmission and reception is notallowed between wireless power transmitter and receiver having different‘profiles’. A profile may be defined according to compatibility and/orapplication irrespective (or independently) of a power class.

For example, profiles may be divided into four types: i) mobile, ii)power tool, iii) kitchen, and iv) wearable profile.

In the case of ‘mobile’ profile, PC may be defined as PC0 and/or PC1;communication protocol/method as IB and OOB; operating frequency as 87to 205 kHz; and application examples may include smartphone and laptopcomputer.

In the case of ‘power tool’ profile, PC may be defined as PC1;communication protocol/method as IB; operating frequency as 87 to 145kHz; and application examples may include a power tool.

In the case of ‘kitchen’ profile, PC may be defined as PC2;communication protocol/method as NFC; operating frequency as being lessthan 100 kHz; and application examples may include kitchen/homeappliances.

In the case of ‘wearable’ profile, PC may be defined as PC-1;communication protocol/method as IB; operating frequency as 87 to 205kHz; and application examples may include wearable devices attached tothe human body.

Maintaining compatibility between the same profiles may be mandatorywhile maintaining compatibility between different profiles may beoptional.

The profiles (mobile, power tool, kitchen, and wearable profiles) may begeneralized to the first to the n-th profiles, and a new profile may beadded or replace an arbitrary one according to the WPC specification andembodiment.

If a profile is defined as described above, a wireless power transmittertransmits power selectively only to the wireless power receivers of thesame profile as the wireless power transmitter, thereby allowing powertransmission to be performed more reliably. Also, since a burden on awireless power transmitter is relieved, and power transmission to anincompatible wireless power receiver is not attempted, an advantageouseffect is obtained that a risk of damaging a wireless power receiver isreduced.

The PC1 within the ‘mobile’ profile may be defined based on the PC0 byadopting selective expansion such as OOB while the ‘power tool’ profilemay be defined by a simply modified version of the PC1 ‘mobile’ profile.Also, the profiles have been defined for the purpose of maintainingcompatibility between the same profiles so far; in a future, however,the technology may be advanced in a direction to maintain compatibilitybetween different profiles. A wireless power transmitter or wirelesspower receiver may inform the other of its profile through variousmeans.

The AFA standard refers to a wireless power transmitter as a powerTransmitting Unit (PTU) and a wireless power receiver as a PowerReceiving Unit (PRU). PUTs are classified to a plurality of classes asshown in Table 1 while PRUs are classified to a plurality of categoriesas shown in Table 2.

TABLE 1 Requirement for Minimum value for the supporting maximum numberof P_(TX) _(—) _(IN) _(—) _(MAX) minimum category supported devicesClass 1  2 W 1x category 1 1x category 1 Class 2 10 W 1x category 3 2xcategory 2 Class 3 16 W 1x category 4 2x category 3 Class 4 33 W 1xcategory 5 3x category 3 Class 5 50 W 1x category 6 4x category 3 Class6 70 W 1x category 7 5x category 3

TABLE 2 PRU P_(TX) _(—) _(OUT) _(—) _(MAX) Example application Category1 TBD Bluetooth headset Category 2 3.5 W Feature phone Category 3 6.5 WSmartphone Category 4 13 W Tablet, pablet Category 5 25 W Small formfactor laptop computer Category 6 37.5 W General laptop computerCategory 7 50 W Home appliance

As shown in Table 1, the maximum output power capability of a class nPTU is larger than or equal to the P_(TX_IN_MAX) of the correspondingclass. A PRU may not draw power larger than that specified in thecorresponding category. FIG. 4 illustrates a block diagram of a wirelesspower transfer system according to another embodiment of the presentinvention.

Referring to FIG. 4, a wireless power transfer system 10 comprises amobile device 450 receiving power wirelessly and a base station 400transmitting power wirelessly.

The base station 400 is an apparatus providing inductive or resonantpower and may include at least one wireless power transmitter 100 and asystem unit 405. The wireless power transmitter 100 may transmitinductive or resonant power and control the transmission. The wirelesspower transmitter 100 may include a power conversion unit 110 whichconverts electric energy to a power signal by generating a magneticfield through a primary coil(s) and a communication & control unit 120which controls communication with and transmission of power to thewireless power receiver 200 so that power may be transmitted at anappropriate level. The system unit 405 may perform control ofmiscellaneous operations of the base station 100, such as input powerprovisioning, control of a plurality of wireless power transmitters, andcontrol of a user interface.

The primary coil may generate an electromagnetic field by usingalternating power (or voltage or current). The primary coil may receivealternating power (or voltage or current) at a specific frequencyproduced at the power conversion unit 110 and accordingly generate amagnetic field of the specific frequency. A magnetic field may begenerated in a non-radial or radial direction, which is received by thewireless power receiver 200 to generate a current. In other words, theprimary coil transmits power wirelessly.

When magnetic induction is used, the primary and secondary coils mayhave any relevant shape and may be constructed by being wound around astructure of high permeability such as ferrite or amorphous metal. Theprimary coil may also be called a primary core, primary winding, orprimary loop antenna. Meanwhile, the secondary coil may also be called asecondary coil, secondary winding, secondary loop antenna, or pickupantenna.

When magnetic resonance is used, the primary and secondary coils may beprovided in the form of a primary resonant antenna and a second resonantantenna, respectively. A resonant antenna may be built from a resonantstructure including a coil and capacitor. At this time, the resonantfrequency of the resonant antenna is determined by inductance of thecoil and capacitance of the capacitor. Here, the coil may be in the formof a loop. Also, a core may be disposed inside the loop. The type ofcore may include a physical core such as one made of ferrite core; or anair core.

Energy transfer between the primary resonant antenna and secondaryresonant antenna may be achieved through magnetic resonance. Magneticresonance refers to the phenomenon where, when one resonant antennagenerates a near-field corresponding to the resonant frequency, andanother resonant antenna is located around the near field, the tworesonant antennas are coupled to each other, and energy transfer with ahigh efficiency is performed between the resonant antennas. If amagnetic field corresponding to a resonant frequency is generatedbetween the primary resonant antenna and the secondary resonant antenna,the primary and secondary resonant antennas resonate with each other.Accordingly, the magnetic field generated by the first resonant antennais concentrated to the secondary resonant antenna with a higherefficiency than the general case where a magnetic field generated by theprimary resonant antenna is radiated to the free space, and therebyenergy may be transmitted from the primary resonant antenna to thesecond resonant antenna with a high efficiency. Magnetic induction maybe achieved in a similar manner as magnetic resonance, but in this case,the frequency of a magnetic field doesn't have to be the resonantfrequency. In the magnetic induction, however, matching of loops formingthe primary and secondary coils is needed, and the spacing between theloops has to be very close.

Although not shown in the figure, the wireless power transmitter 1100may further include a communication antenna. A communication antenna maytransmit and receive a communication signal by using a communicationcarrier in addition to magnetic field communication. For example, acommunication antenna may transmit and receive communication signalssuch as a WiFi, Bluetooth, Bluetooth LE, ZigBee, and NFC signal.

The communication & control unit 120 may transmit and receiveinformation to and from the wireless power receiver 200. Thecommunication/control unit 120 may include at least one of the IB or OOBcommunication module.

The IB communication module transmits and receives information by usinga magnetic wave having a specific frequency as its center frequency. Forexample, the communication & control unit 120 may perform in-bandcommunication by placing information in a magnetic wave and transmittingthe information through the primary coil or receiving a magnetic wavecarrying information through the primary coil. At this time, informationmay be placed in a magnetic wave or interpret a magnetic wave carryinginformation by using a modulation method such as binary phase shiftkeying (BPSK) or amplitude shift keying (ASK) or a coding method such asManchester coding or non-return-to-zero level (NZR-L) coding. By usingthe IB communication, the communication & control unit 120 may transmitand receive information up to several meters at a data transmission rateof a few kbps.

The OOB communication module may perform out-band communication througha communication antenna. For example, the communication & control unit120 may be provided as a short range communication module. Examples of ashort range communication module include a WiFi, Bluetooth, BluetoothLE, ZigBee, and NFC module.

The communication & control unit 120 may control the overall operationof the wireless power transmitter 100. The communication & control unit120 may perform computation and processing of various types ofinformation and control each individual element of the wireless powertransmitter 100.

The communication & control unit 120 may be implemented by a computer ora device similar to the computer by using hardware, software, or acombination of both. In a hardware form, the communication & controlunit 120 may be provided in the form of an electronic circuit whichperforms a control function by processing an electric signal, and in asoftware form, the communication & control unit 120 may be provided inthe form of a program which drives the communication & control unit 120.

The communication & control unit 120 may control transmission power bycontrolling an operating point. The controlled operating point maycorrespond to a combination of frequency (or phase), duty cycle, dutyratio, and voltage amplitude. The communication & control unit 120 maycontrol transmission power by adjusting at least one of frequency (orphase), duty cycle, duty ratio, and voltage amplitude. Also, thewireless power transmitter 100 may provide a predetermined power, andthe wireless power receiver 200 may control a received power bycontrolling the resonant frequency.

The mobile device 450 includes a wireless power receiver 200 whichreceives wireless power through the secondary coil and a load 455 whichstores the power received by the wireless power receiver 200 andprovides power to the load 455.

The wireless power receiver 200 may include a power pick-up unit 210 andcommunication & control unit 220. The power pick-up unit 210 may receivewireless power through the secondary coil and convert the received powerto electric energy. The power pick-up unit 210 rectifies an alternatingcurrent signal obtained through the secondary coil to convert the ACsignal to a DC signal. The communication & control unit 220 may controltransmission and reception of wireless power (transmission and receptionof power).

The secondary coil may receive wireless power transmitted from thewireless power transmitter 100. The secondary coil may receive power byusing a magnetic field generated by the primary coil. Here, if aspecific frequency is a resonant frequency, magnetic resonance isdeveloped between the primary and secondary coils, and power may betransmitted more efficiently.

Although not shown in FIG. 4, the communication/control unit 220 mayfurther include a communication antenna. The communication antenna maytransmit and receive a communication signal by using a communicationcarrier in addition to magnetic field communication. For example, acommunication antenna may transmit and receive a communication signalsuch as a WiFi, Bluetooth, Bluetooth LE, ZigBee, or NFC signal.

The communication & control unit 220 may transmit and receiveinformation to and from the wireless power transmitter 100. Thecommunication/control unit 220 may include at least one of the IB or OOBcommunication module.

The IB communication module transmits and receives information by usinga magnetic wave having a specific frequency as its center frequency. Forexample, the communication & control unit 220 may perform in-bandcommunication by placing information in a magnetic wave and transmittingthe information through the secondary coil or receiving a magnetic wavecarrying information through the secondary coil. At this time,information may be placed in a magnetic wave or interpret a magneticwave carrying information by using a modulation method such as binaryphase shift keying (BPSK) or amplitude shift keying (ASK) or a codingmethod such as Manchester coding or non-return-to-zero level (NZR-L)coding. By using the IB communication, the communication & control unit220 may transmit and receive information up to several meters at a datatransmission rate of a few kbps.

The OOB communication module may perform out-band communication througha communication antenna. For example, the communication & control unit220 may be provided as a short range communication module.

Examples of a short range communication module include a WiFi,Bluetooth, Bluetooth LE, ZigBee, and NFC module.

The communication & control unit 220 may control the overall operationof the wireless power transmitter 100. The communication & control unit220 may perform computation and processing of various types ofinformation and control each individual element of the wireless powerreceiver 200.

The communication & control unit 220 may be implemented by a computer ora device similar to the computer by using hardware, software, or acombination of both. In a hardware form, the communication & controlunit 220 may be provided in the form of an electronic circuit whichperforms a control function by processing an electric signal, and in asoftware form, the communication & control unit 220 may be provided inthe form of a program which drives the communication & control unit 120.

The load 455 may be a battery. A battery may store energy by using powerproduced from the power pick-up unit 210. Meanwhile, a battery does notnecessarily have to be included in the mobile device 450. For example,the battery may be provided as an external entity that may be attachedto or detached from the mobile device 450. In another example, thewireless power receive 200 may include a driving means which drivesvarious operations of an electronic device in the place of the battery.

Although it is shown in the figure that the mobile device 450 includesthe wireless power receiver 200, and the base station 400 includes thewireless power transmitter 100, the wireless power receiver 200 may beconsidered to be the same as the mobile device 450, and the wirelesspower transmitter 100 may also be considered to be the same as the basestation 400.

In what follows, the coil or coil unit may also be referred to as a coilassembly, coil cell, or cell by including a coil and at least oneelement adjacent to the coil.

FIG. 5 is a state transition diagram illustrating a wireless powertransfer procedure.

Referring to FIG. 5, power transfer from a wireless power transmitter toa receiver according to one embodiment of the present invention maylargely comprise a selection phase 510, ping phase 520, identificationand configuration phase 530, negotiation phase 540, calibration phase550, power transfer phase 560, and renegotiation phase 570.

If power transfer is started or a specific error or specific event isdetected while power transfer is conducted, the wireless powertransmitter transitions to the selection phase 510 which includes, forexample, S502, S504, S508, S510, and S512. Here, a specific error andspecific event may be clearly understood through descriptions givenbelow. Also, in the selection phase 510, a wireless power transmittermay monitor whether an object exists on the interface surface. If thewireless power transmitter detects that an object is placed on thesurface of the interface, the wireless power transmitter may transitionto the ping phase 520. In the selection phase 510, the wireless powertransmitter may transmit an analog ping signal composed of very shortpulses and detect whether an object exists on an active area of theinterface surface based on a current change of a transmitter coil orprimary coil.

If an object is detected in the selection phase 510, the wireless powertransmitter may measure the quality factor (Q factor) of a wirelessresonance circuit (for example, power transfer coil and/or resonantcapacitor). In one embodiment of the present invention, if an object isdetected in the selection phase 510, the Q factor may be measured todetermine whether a wireless power receiver is placed in a charging areatogether with a foreign object. Inductance and/or series resistancevalue of a coil included in the wireless power transmitter may bereduced due to a change of the surroundings, which accordingly reducesthe Q factor. To determine existence of a foreign object by using themeasured Q factor, the wireless power transmitter may receive, from thewireless power receiver, a reference Q factor measured previously when aforeign object is not placed in the charging area. In the negotiationphase S540, existence of a foreign object may be determined by comparingthe received reference Q factor with the measured Q factor. However, inthe case of a wireless power receiver the reference Q factor of which islow—as one example, a specific wireless power receiver may have a low Qfactor depending on its type, use, and characteristics, existence of aforeign object may not be readily determined since there is not anoticeable difference between a Q factor measured in the presence of aforeign object and the reference Q factor. Therefore, existence of aforeign object has to be determined by taking into account anotherdetermination factor or by using another method.

In another embodiment of the present invention, if an object is detectedin the selection phase 510, a Q factor within a specific frequency area(for example, an operating frequency area) may be measured to determinewhether a foreign object is disposed together in the charging area.Inductance and/or series resistance value of the coil of the wirelesspower transmitter may be reduced due to a change of the surroundings,which accordingly changes (shifts) the resonant frequency of the coil ofthe wireless power transmitter. In other words, the Q factor peakfrequency may be shifted, where the Q factor peak frequency is afrequency at which the maximum Q factor is measured within the operatingfrequency area.

In the ping phase 520, if an object is detected, the wireless powertransmitter wakes up the receiver and transmits a digital ping signal toidentify whether the detected object is a wireless power receiver. Ifthe wireless power transmitter fails to receive a response signal—forexample, a signal strength packet—in response to the digital pingsignal, power transfer may transition again to the selection phase 510.Also, in the ping phase 520, if the wireless power transmitter receives,from the receiver, a signal indicating that power transfer has beencompleted—namely, a charging completion packet, power transfer maytransition to the selection phase 510.

If the ping phase 520 is completed, the wireless power transmitter maytransition to the identification & configuration phase 530 foridentifying the receiver and collecting structure and state informationof the receiver.

In the identification & configuration phase 530, if an unexpected packetis received (unexpected packet), a desired packet is not received for apredetermined time period (time out), a packet transmission error isoccurred (transmission error), or power transfer contract is notestablished (no power transfer contact), the wireless power transmittermay transition to the selection phase 510.

The wireless power transmitter may check whether transition to thenegotiation phase 540 is needed based on a negotiation field value ofthe configuration packet received in the identification & configurationphase 530. If it is determined from the checking result that anegotiation is needed, the wireless power transmitter may transition tothe negotiation phase 540 and perform a predetermined FOD detectionprocedure. On the other hand, if it is determined from the checkingresult that a negotiation is not required, the wireless powertransmitter may immediately transition to the power transfer phase 560.

In the negotiation phase, the wireless power transmitter may receive aforeign object detection (FOD) state packet including a reference Qfactor. Or the wireless power transmitter may receive an FOD statepacket including a reference peak frequency value. Or the wireless powertransmitter may receive a state packet including the reference Q factorand reference peak frequency value. At this time, the wireless powertransmitter may determine a Q factor threshold value for detecting aforeign object (FO) based on the reference Q factor value. The wirelesspower transmitter may determine a peak frequency threshold for detectinga foreign object (FO) based on the reference peak frequency value.

The wireless power transmitter may detect whether an FO exists in thecharging area by using the determined Q factor threshold for detectingan FO and a currently measured Q factor (the Q factor value measuredbefore the ping phase) and control power transfer according to theresult of FO detection. As one example, when an FO is detected, powertransfer may be stopped, but the present invention is not limited to theparticular case.

The wireless power transmitter may detect whether an FO exists in thecharging area by using the determined peak frequency threshold fordetecting an FO and a currently measured peak frequency value (the peakfrequency value measured before the ping phase) and control powertransfer according to the result of FO detection. As one example, whenan FO is detected, power transfer may be stopped, but the presentinvention is not limited to the particular case.

When an FO is detected, the wireless power transmitter may return to theselection phase 510. On the other hand, if an FO is not detected, thewireless power transmitter goes through the calibration phase 550 toenter the power transfer phase 560. More specifically, if no FO isdetected, the wireless power transmitter may determine strength of powerreceived by the receiver at the calibration phase 550 and measure powerloss at the receiver and transmitter to determine strength of powertransmitted by the transmitter. In other words, the wireless powertransmitter may predict power loss based on the difference betweentransmitted power of the transmitter and received power of the receiverat the calibration phase 550. The wireless power transmitter accordingto one embodiment of the present invention may adjust the threshold fordetecting an FO by reflecting the predicted power loss.

In the power transfer phase 560, if an unexpected packet is received(unexpected packet), a desired packet is not received for apredetermined time period (time out), a pre-configured power transfercontract is violated (power transfer contract violation), or charging iscompleted, the wireless power transmitter may transition to theselection phase 510.

Also, in the power transfer phase 560, if it is needed to reconfigure apower transfer contract according to a state change of the wirelesspower transmitter, the wireless power transmitter may transition to therenegotiation phase 570. At this time, renegotiation is completednormally, the wireless power transmitter may return to the powertransfer phase 560.

The power transfer contract may be configured based on the state of thewireless power transmitter and receiver and characteristic information.As one example, state information of the wireless power transmitter mayinclude the maximum amount of power that may be transmitted and themaximum number of receivers that may be accommodated while stateinformation of the receiver may include required power.

FIG. 6 illustrates a power control method according to one embodiment ofthe present invention.

In the power transfer phase 560 of FIG. 6, the wireless powertransmitter 100 and wireless power receiver 200 may control the amountof power transmitted by performing power transmission and reception inconjunction with communication. The wireless power transmitter andwireless power receiver operate at a specific control point. A controlpoint represents a combination of voltage and current provided at theoutput terminal of the wireless power receiver when power transfer isperformed.

To describe in more detail, the wireless power receiver selects adesired control point—a desired output current/voltage or temperate of amobile device at a specific position—and additionally determines anactual control point that is currently operating. The wireless powerreceiver may calculate a control error value by using the desired andactual control points and transmit the calculated control error value tothe wireless power transmitter in the form of a control error packet.

And the wireless power transmitter may control power transfer byconfiguring/controlling a new operating point—amplitude, frequency, andduty cycle—by using a received control error packet. Therefore, thecontrol error packet is transmitted/received at predetermined timeintervals at the power transfer phase, and as an embodiment, thewireless power receiver may transmit a control error by setting thecontrol error to a negative value in order to reduce the current of thewireless power transmitter but setting the control error as a positivevalue in order to increase the current. As described above, in aninduction mode, the wireless power receiver may control power transferby transmitting a control error packet to the wireless powertransmitter.

In a resonance mode to be described below, power transfer may beperformed differently from the induction mode. In the resonance mode,one wireless power transmitter is required to serve a plurality ofwireless power receivers simultaneously. However, since power transferin the induction mode is controlled by communication with one wirelesspower receiver, it may be difficult to control power transfer toadditional wireless power receivers. Therefore, in the resonance modeaccording to the present invention, a wireless power transmittertransmits predetermined power commonly to wireless power receivers, anda wireless power receiver controls the amount of power to receive bycontrolling its own resonant frequency. However, it should be noted thatthe method described with reference to FIG. 6 is not completely excludedfrom the operations in the resonance mode; rather, control of additionalpower transfer may be performed according to the method of FIG. 6.

FIG. 7 illustrates a block diagram of a wireless power transmitteraccording to another embodiment of the present invention. The wirelesspower transmitter may belong to a wireless power transfer system in amagnetic resonance or shared mode. A shared mode may refer to the modein which a wireless power transmitter performs one-to-many communicationand charging with wireless power receivers. The shared mode may beimplemented by employing a magnetic induction or resonance method.

Referring to FIG. 7, the wireless power transmitter 700 may include atleast one of a cover 720 covering a coil assembly, power adaptor 730which provides power to a power transmitting unit 740, powertransmitting unit 740 which transmits power wirelessly, or userinterface 750 providing information related to progress of powertransfer or other matters. In particular, the user interface 750 may beincluded optionally or included as other user interface 750 of thewireless power transmitter 700.

The power transmitting unit 740 may include at least one of a coilassembly 760, impedance matching circuit 770, inverter 780,communication unit 790, or control unit 710.

The coil assembly 760 includes at least one primary coil generating amagnetic field, which may also be called a coil cell.

The impedance matching circuit 770 may provide impedance matchingbetween the inverter and primary coil(s). The impedance matching circuit770 may generate resonance at a suitable frequency for boosting aprimary coil current. The impedance matching circuit of a multi-coilpower transmitting unit 740 may further include a multiplexing elementwhich routes a signal to a subset of primary coils of the inverter. Theimpedance matching circuit may also be called a tank circuit.

The impedance matching circuit 770 may include capacitor, inductor, andswitching element which switches a connection thereof. Impedancematching may be performed by detecting a reflective wave of wirelesspower transmitted through the coil assembly 760, adjusting theconnection state of capacitor or inductor by switching the switchingelement based on the detected reflective wave, adjusting capacitance ofthe capacitor, or adjusting inductance of the inductor. Depending on thesituations, the impedance matching circuit 770 may be omitted, and thepresent specification includes embodiments of the wireless powertransmitter 700 from which the impedance matching circuit 770 isomitted.

The inverter 780 may convert a DC input to an AC signal. The inverter780 may use a half-bridge or full-bridge to generate a pulse wave andduty cycle of an adjustable frequency. Also, the inverter may include aplurality of stages to adjust an input voltage level.

The communication unit 790 may perform communication with a powerreceiver. The power receiver performs load modulation to communication arequest and information about a power transmitter and information.Therefore, the power transmitter 740 may monitor a current and/orvoltage amplitude and/or phase of the primary coil to demodulate thedata transmitted by the power receiver by using the communication unit790.

Also, the power transmitter 740 may also control output power totransmit data by using a frequency shift keying method through acommunication unit 790.

The control unit 710 may control communication and power transfer of thepower transmitter 740. The control unit 710 may control power transferby adjusting the aforementioned operating point. The operating point maybe determined by at least one of an operating frequency, duty cycle, andinput voltage, for example.

The communication unit 790 and control unit 710 may be implemented as aseparate unit/element/chipset or as a single unit/element/chipset.

FIG. 8 illustrates a wireless power receiver according to anotherembodiment of the present invention. The wireless power receiver maybelong to a wireless power transfer system in a magnetic resonance orshared mode.

In FIG. 8, the wireless power receiver 800 may include at least one of auser interface 820 providing information about progress of powertransfer and other matters, power receiving unit 830 receiving wirelesspower, load circuit 840, or base 850 supporting and covering a coilassembly. In particular, the user interface 750 may be includedoptionally or included as other user interface 750 of the wireless powertransmitter 700.

The power receiving unit 830 may include at least one of a powerconverter 860, impedance matching circuit 870, coil assembly 880,communication unit 890, or control unit 810.

The power converter 860 may convert AC power received from the secondarycoil to a voltage and current suitable for the load circuit. As anembodiment, the power converter 860 may include a rectifier. Therectifier may rectify received wireless power and convert the receivedpower from AC to DC. The rectifier may convert the received power fromAC to DC by using a diode or transistor and equalize the converted powerby using capacitor and resistor. The rectifier may use a full-rectifierimplemented by a bridge circuit, half-rectifier, voltage multiplier, andso on. In addition, the power converter may adapt reflected impedance ofthe power receiver.

The impedance matching circuit 870 may provide impedance matchingbetween a combination of the power converter 860 and load circuit 870;and the secondary coil. As an embodiment, the impedance matching circuitmay generate resonance at around 100 kHz which may reinforce powertransfer. The impedance matching circuit 870 may include capacitor,inductor, and switching element which switches a connection thereof.Impedance matching may be performed by controlling a switching elementof the impedance matching circuit 870 based on a voltage, current,power, and frequency value of received wireless power. Depending on thesituations, the impedance matching circuit 870 may be omitted, and thepresent specification includes embodiments of the wireless powerreceiver 200 from which the impedance matching circuit 870 is omitted.

The coil assembly 880 includes at least one secondary coil and mayfurther include an optional element which shields a metallic portion ofthe receiver from a magnetic field.

The communication unit 890 may perform load modulation to communicate arequest and other information to the power transmitter.

To this purpose, the power receiving unit 830 may switch resistor orcapacitor to change reflective impedance.

The control unit 810 may control received power. To this purpose, thecontrol unit 810 may determine/calculate a difference between an actualoperating point and desired operating point of the power receiving unit830. And the control unit 810 may adjust/reduce a difference between theactual operating point and desired operating point by fulfilling arequest for adjusting reflective impedance and/or an operating point ofthe power transmitter. When the difference is minimized, optimal powerreception may be performed.

The communication unit 790 and control unit 810 may be implemented as aseparate unit/element/chipset or as a single unit/element/chipset.

FIG. 9 illustrates a communication frame structure according to oneembodiment of the present invention. The communication frame structuremay be in the shared mode.

Referring to FIG. 9, in the shared mode, different forms of frames maybe used together. For example, in the shared mode, a slotted framehaving multiple slots as shown in (A) and a free format frame which doesnot have a specific form as shown in (B) may be used. More specifically,a slotted frame is aimed for transmitting short data packets from awireless power receiver 200 to a wireless power transmitter 100, and afree format frame is capable of transmitting long data packets sincemultiple slots are not used.

Meanwhile, a slotted frame and free format frame may be changed tovarious names by those skilled in the art. For example, the slotted maybe called a channel frame, and the free format frame may be called amessage frame.

More specifically, the slotted frame may include a sync patternindicating the start of a slot, measurement slot, 9 slots, and anadditional sync pattern having the same time interval before each of the9 slots.

At this time, the additional sync pattern is a sync pattern differentfrom the one indicating the start of a frame described above. Morespecifically, the additional sync pattern may show information relatedto adjacent slots (namely two consecutive slots located at both sides ofa sync pattern) without showing the start of a frame.

Among the 9 slots, a sync pattern may be placed between two consecutiveslots. In this case, the sync pattern may provide information related tothe two consecutive slots.

Also, the 9 slots and sync patterns provided before the respective 9slots may have the same time interval. For example, the 9 slots may havea time interval of 50 ms. Also, the 9 sync patterns may also have timeduration of 50 ms.

Meanwhile, the free format frame as shown in (B) may not have a specificform except for a sync pattern indicating the start of a frame and ameasurement slot. In other words, the free format frame is aimed toperform the role different from the slot frame and may be used toperform communication of long data packets (for example, additionalowner information packets) between the wireless power transmitter andwireless power receiver or perform selecting one coil from among aplurality of coils in a wireless power transmitter composed of aplurality of coils.

In what follows, the sync pattern included in each frame will bedescribed in more detail with reference to appended drawings.

FIG. 10 illustrates a structure of a sync pattern according to oneembodiment of the present invention.

Referring to FIG. 10, a sync pattern may comprise a preamble, start bit,response field, type field, info field, and parity bit. In FIG. 10, astart bit is denoted as ZERO.

More specifically, a preamble is composed of consecutive bits which mayall be set to 0. In other words, a preamble may be composed of bit forsetting time duration of a sync pattern.

The number of bits comprising a preamble may depend on an operatingfrequency so that the length of a sync pattern is close to 50 ms as muchas possible but not exceeding 50 ms. For example, when the operatingfrequency is 100 kHz, the sync pattern may be composed of two preamblebits while, when the operating frequency is 105 kHz, the sync patternmay be composed of three preamble bits.

The start bit follows next to the preamble and may indicate ZERO. TheZERO may be a bit indicating the type of the sync pattern. Here, thetype of sync pattern may include a frame sync including informationrelated to a frame and a slot sync including information of a slot. Inother words, the sync pattern may be a frame sync being located betweenconsecutive frames and representing the start of a frame or a slot syncbeing located between consecutive slots among a plurality of slotsconstituting a frame and including information related to theconsecutive slots.

For example, when the ZERO is 0, it may indicate that the correspondingslot is a slot sync located between slots while, when the ZERO is 1, itmay indicate that the corresponding sync pattern is a frame sync locatedbetween frames.

The parity bit is the last bit of a sync pattern, which may representthe number of bits constituting data fields (in other words, a responsefield, type field, and information field) of the sync pattern. Forexample, the parity bit may be 1 when the number of bits constitutingthe data fields of a sync pattern is an even number and 0, otherwise(namely when the number of bits is an odd number).

The response field may include response information of a wireless powertransmitter with respect to communication with a wireless power receiverwithin a slot before the sync pattern. For example, the response fieldmay have a value of ‘00’ if no activity of communication with a wirelesspower receiver is detected. Also, if a communication error is detectedduring communication with a wireless power receiver, the response fieldmay have a value of ‘01’. The communication error may be generated whentwo or more wireless power receivers attempt to access one slot, and acollision is occurred among two or more wireless power receivers.

Also, the response field may include information indicating whether adata packet has been received correctly from a wireless power receiver.More specifically, if a wireless power transmitter denies a data packet,the response field may have a value of “10” (10—not acknowledge, NAK)while, if the wireless power transmitter confirms the data packet, theresponse field may have a value of “11” (11-acknowledge, ACK).

The type field may represent the type of a sync pattern. Morespecifically, the type field may have a value of ‘1’ indicating a framesync when a sync pattern is the first sync pattern of a frame (in otherwords, when the sync pattern is the first sync pattern of a frame andlocated before a measurement slot).

Also, when a sync pattern is not the first sync pattern of a frame, thetype field may have a value of ‘0’ indicating a slot sync.

Also, the information field may be interpreted differently according tothe type of a sync pattern indicated by the type field. For example,when the type field is 1 (namely, the type field indicates a framesync), the information field may indicate the type of a frame. In otherwords, the information field may represent whether a current frame is aslotted frame or free-format frame. For example, if the informationfield is ‘00’, it indicates a slotted frame while, if the informationfield is ‘01’, it indicates a free-format frame.

Differently from the description above, if the type field is 0 (namelyin the case of a slot sync), the information field may represent thestate of the next slot located after the sync pattern. Morespecifically, the information field may have a value of ‘00’ when thenext slot is a slot allocated to a specific wireless power receiver;‘01’ when the next slot is a slot locked temporarily to be used by thewireless power receiver; and ‘10’ when the next slot is a slot which maybe used freely by an arbitrary wireless power receiver.

FIG. 11 illustrates operation states of a wireless power transmitter andwireless power receiver in a shared mode according to one embodiment ofthe present invention.

Referring to FIG. 11, a wireless power receiver operating in the sharedmode may operate in one of the phases among selection phase 1100,introduction phase 1110, configuration phase 1120, negotiation phase1130, and power transfer phase 1140.

First, a wireless power transmitter according to one embodiment of thepresent invention may transmit a wireless power signal to detect awireless power receiver. In other words, a process for detecting awireless power receiver by using a wireless power signal may be calledanalog ping.

Meanwhile, the wireless power receiver which has received a wirelesspower signal may enter the selection phase 1100. The wireless powerreceiver which has entered the selection state 1100, as described above,may detect existence of an FSK signal on the wireless power signal.

In other words, the wireless power receiver may perform communicationaccording to the exclusive or shared mode depending on existence of anFSK signal.

More specifically, the wireless power receiver operates in the sharedmode if an FSK signal is included in a wireless power signal orotherwise operates in the exclusive mode.

When the wireless power receiver operates in the shared mode, thewireless power receiver may enter the introduction phase 1110. In theintroduction phase 1110, the wireless power receiver may transmit acontrol information packet to the wireless power transmitter to transmita control information (CI) packet in the configuration, negotiation, andpower transfer phases. The control information packet may have a headerand control-related information. For example, the control informationpacket may have a header the value of which is 0X53.

In the introduction phase 1110, the wireless power receiver performs anattempt for requesting a free slot to transmit the control information(CI) packet throughout the subsequent configuration, negotiation, andpower transfer phases. At this time, the wireless power receiver selectsa free slot and transmits an initial CI packet. If the wireless powertransmitter responds with an ACK to the corresponding CI packet, thewireless power transmitter enters the configuration phase. If thewireless power transmitter responds with a NACK, it indicates that thewireless power transmitter is performing the configuration andnegotiation phases in conjunction with other wireless power receiver. Inthis case, the wireless power receiver re-attempts the request for afree slot.

If the wireless power receiver receives an ACK in response to the CIpacket, the wireless power receiver determines the position of a privateslot within a frame by counting the remaining slot syncs up to theinitial frame sync. For all of the subsequent slot-based frames, thewireless power receiver transmits the CI packet through thecorresponding slot.

If the wireless power transmitter allows the wireless power receiver toenter the configuration phase, the wireless power transmitter provides aseries of locked slots for an exclusive use of the wireless powerreceiver. By doing so, the wireless power receiver may be ensured toenter the configuration phase without a collision.

The wireless power receiver transmits sequences of data packets such astwo identification data packets (IDHI and IDLO) by using a locked slot.Once the present phase is completed, the wireless power receiver entersthe negotiation phase. In the negotiation phase, the wireless powertransmitter still provides a locked slot for an exclusive use of thewireless power receiver. This ensures that the wireless power receiverperforms the negotiation phase without a collision.

The wireless power receiver transmits one or more negotiation datapackets by using the corresponding locked slot, which may be mixed withprivate data packets. As a result, the corresponding sequence isterminated along with a specific request (SRQ) packet. If thecorresponding sequence is completed, the wireless power receiver entersthe power transfer phase and stops providing a locked slot.

In the power transfer phase, the wireless power receiver performstransmission of a CI packet and receives power by using an allocatedslot. The wireless power receiver may include a regulator circuit. Theregulator circuit may be included in the communication & control unit.The wireless power receiver may self-regulate the reflective impedanceof the wireless power receiver through the regulator circuit. In otherwords, the wireless power receiver may adjust the reflective impedanceto transmit as much power as required by an external load. By doing so,reception of excessive power and overheating may be prevented.

In the shared mode, the wireless power transmitter may not performadjusting power in response to a received CI packet (depending on theoperation mode); in this case, control may be needed to prevent anovervoltage condition.

In what follows, an apparatus and method for performing detection of aforeign object in a wireless power transfer system and a method fortesting foreign object detection performance of a wireless powerreceiver will be disclosed.

Detection of a foreign object may be performed in various ways. Awireless power transmitter and/or receiver may perform foreign objectdetection during the power transfer phase or perform foreign objectdetection before the power transfer phase. In particular, in the case ofan extended power profile (EPP) which requires relatively large powerconsumption or a wireless power receiver at medium power level, afunction of detecting a foreign object even before the power transferphase is needed. In other words, foreign object detection may beperformed in the negotiation phase which precedes the power transferphase. For example, if a wireless power receiver transmits a reference Qfactor to a wireless power transmitter in the negotiation phase, thewireless power transmitter may determine whether a foreign object existson the interface surface of the wireless power transmitter by using thereference Q factor.

However, even though there actually exists a foreign object, if thewireless power transmitter wrongly concludes that there is no foreignobject even in the negotiation phase, the wireless power transmitterenters the power transfer phase, and system calibration is performed.Afterwards, the wireless power transmitter transmits wireless powercontinuously to the wireless power receiver based on the wrong decisionon the foreign object detection, which may eventually lead to anaccident such as overheating. As described above, a failure of properdetection of a foreign object may be caused by a difference in theindividual characteristics of wireless power receivers. For example, inthe case of a wireless power receiver the reference Q factor of which islow—as one example, a specific wireless power receiver may have a low Qfactor depending on its type, use, and characteristics, existence of aforeign object may not be readily determined since there is not anoticeable difference between a Q factor measured in the presence of aforeign object and the reference Q factor.

As an example of a wireless power receiver, Table 3 shows reference Qfactors of various mobile devices (Q factors when there is no foreignobject in the surroundings) and a measurement result of Q factors ofreference wireless power transmitters or test power transmitters (TPTs)when there exist predefined, various types of representative foreignobjects (RFOs).

TABLE 3 Q-factor measured by LCR meter Mobile device without FO RFO#1RFO#2 RFO#3 RFO#4 None 160 49.5 37.1 31 50 A 55 23.7 24.2 20 29 B 4724.2 25.8 20.1 29 C 46 24.8 25 20 31 D 54 25.7 25.9 21.1 32 E 60 33.831.8 26.9 39.5 F 57 26.2 26.9 21.8 31 G 80 36 32.8 27.3 40.6 H 66 32.330 25.5 36.5 I 106 33.6 29.1 24.6 36 J 56 24.5 22.6 19.3 27.5 K 29 21.623.8 19.4 29 L 20 20.7 22.9 18.9 24 M 25 31.9 32.2 29.1 33

Referring to Table 3, when there is no mobile device (None), it ismeasured that the Q factor when there is no foreign object (without FOin the table) is 160; the Q factor when there exists a firstrepresentative foreign object (RFO #1) is 49.5; the Q factor when thereexists a second representative foreign object (RFO #2) is 37.1; the Qfactor when there exists a third representative foreign object (RFO #3)is 31; and the Q factor when there exists a fourth representativeforeign object (RFO #4) is 50.

Meanwhile, in the case of mobile device “K”, “L”, and “M”, it isobserved that the Q factor is larger than or equal to the Q factor(Q_(RFO #n)) in the presence of a representative foreign object,compared with the Q factor (Q_(w/o FO)) in the absence of a foreignobject. Here, the representative foreign object may be an objectspecified for a compliance test by the WPC standard.

As described above, when there is no noticeable difference between a Qfactor measured in the presence of a foreign object and a reference Qfactor measured in the absence of foreign object, it may be difficult todetermine existence of a foreign object. In this case, existence of aforeign object has to be determined by taking into account anotherdetermination factor or by using another method. Therefore, an apparatusand method for improving accuracy and reliability of detecting a foreignobject irrespective of individual characteristics of a wireless powerreceiver is needed.

In what follows, a result of an experiment and simulation conducted todesign an optimal reference Q factor according to the present embodimentwill be disclosed. The optimal reference Q factor refers to the minimumreference Q factor by which a foreign object may be detectedindependently of the type and characteristics of a mobile device and/ora foreign object.

To design an optimal reference Q factor according to the presentembodiment, four Q factors have been measured in advance. One is areference Q factor (Q_(ref)) that may be obtained from a referencewireless power transmitter when neither a foreign object nor a wirelesspower receiver exists in the surroundings. Another one is a reference Qfactor (Q_(RFO)) that may be obtained from a reference wirelesstransmitter when a wireless power receiver does not exist, but arepresentative foreign object is present in the surroundings. Third oneis related to the case where a wireless power receiver is place on areference wireless power transmitter and corresponds to a first Q factor(Q_(RX)) which is a reference Q factor that may be obtained from areference wireless power transmitter when no representative foreignobject exists in the surroundings. The last one is related to the casewhere a wireless power receiver is placed on a reference wireless powertransmitter and corresponds to a second Q factor (Q_(RX+RFO)) which is areference Q factor that may be obtained from a reference wireless powertransmitter when a representative foreign object exists in thesurroundings.

First, a reference Q factor (Q_(ref)) that may be obtained from areference wireless power transmitter when neither a foreign object nor awireless power receiver exists in the surroundings is derived.

FIG. 12 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter used for an experiment of thepresent embodiment.

Referring to FIG. 12, the power transmitting unit 1200 of a referencewireless power transmitter includes a primary coil 1210 and shieldingunit 1220.

The primary coil 1210 is wound in a planar spiral pattern and may bedisposed on one surface of the shielding unit 1220. A litz coil may beused as the primary coil 1210. The primary coil 1210 and shielding unit1220 model TPT-QFACTOR, and each physical parameter value follows thephysical parameter value related to the TPT-QFACTOR defined in the WPCstandard ver1.2.3.

When an input signal having a frequency of 100 kHz is applied to thepower transmitting unit 1200 having the aforementioned physicalparameter value, measured inductance (L_(REF)) and reference Q factor(Q_(ref)) are given as shown in Table 4.

TABLE 4 Measurement Simulation Symbol Standard result result L_(REF)(μH) 124.8 ± 1 — 25.8 Q_(ref) 157.6 ± 2%~158.6 ± 2% 160 158.3

It may be known from Table 4 that the reference Q factor that may beobtained from a reference wireless power transmitter is 160.

Next, when there exists no wireless power receiver, but a representativeforeign object exists in the surroundings, a reference Q factor(Q_(ref)) that may be obtained from the reference wireless powertransmitter is derived.

FIG. 13 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter; and four representative foreignobjects used for an experiment of the present embodiment.

Referring to FIG. 13, the representative foreign object (RFO #1) used inthe experiment (a) is a disk type steel having a diameter of 15 mm and athickness of 1 mm; the representative foreign object (RFO #2) used inthe experiment (b) is a ring type aluminum having an outer diameter of22 mm, inner radius of 20 mm, and the maximum outer diameter of 26 mm;the representative foreign object (RFO #3) used in the experiment (c) isfoil aluminum having a diameter of 20 mm and a thickness of 0.1 mm; therepresentative foreign object (RFO #4) used in the experiment (d) is adisk type aluminum having a radius of 22 mm and a thickness of 1 mm. Asshown in the lower part of (a), (b), (c), and (d), the Q factor ismeasured while the center of each representative foreign object is madeto be aligned with the center of a reference wireless power transmitter1200, and a vertical spacing between the two centers is kept to 2.5mm+0.5 mm. Here, 2.5 mm is a distance from the upper end of the primarycoil to the interface surface of the reference wireless powertransmitter, and 0.5 mm is a distance from the representative foreignobject to the lower end of the frame.

Table 5 shows a reference Q factor (Q_(RFO)) measured when an inputsignal having a frequency of 100 kHz is applied to each representativeforeign object.

TABLE 5 Reference Q factor (Q_(RFO)) Measurement result Simulationresult RFO#1 49.5 49.5 RFO#2 37.1 34.4 RFO#3 31 27.1 RFO#4 50 51

Considered next is the case when a wireless power receiver is placed ona reference wireless power transmitter; a first Q factor (Q_(RX)) whichis a reference Q factor that may be obtained from the reference wirelesspower transmitter is derived under a condition that no representativeforeign object is present in the surroundings thereof.

FIG. 14 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter; and a secondary coil, shieldingunit, and metal case member of a reference wireless power receiver usedfor an experiment of the present embodiment.

Referring to FIG. 14, the power transmitting unit 1200 of the referencewireless power transmitter includes a primary coil 1210 and shieldingunit 1220, which is the same as shown in FIG. 12.

The power receiving unit 1400 of the reference wireless power receiverincludes a secondary coil 1410, shielding unit 1420, and metal casemember 1430 of a mobile device.

The secondary coil 1410 is wound in a planar spiral pattern and may bedisposed on one surface of the shielding unit 1420. A litz coil may beused as the secondary coil 1410. The secondary coil and shielding unitused in the experiment of the present invention is iPhone X. Also, thehorizontal and vertical length of the metal case member 1430 are 50 mm,respectively.

FIG. 15 shows a first Q factor (Q_(RX)) measured when the thickness(t_(FM)) of the metal case is varied while an input signal with afrequency of 100 kHz is applied to the power transmitting unit 1200having the aforementioned physical parameter values. FIG. 15 is asimulation result according to an embodiment of FIG. 14.

Referring to FIG. 15, “@xmm” indicates that the center of the secondarycoil of the wireless power receiver is separated from the center of thereference wireless power transmitter by x mm. The reference Q factor maybe defined as the smallest value among the total of five Q factorsmeasured by placing the wireless power receiver so that the centerthereof is aligned with the center of the reference wireless powertransmitter, and a vertical spacing between the centers is kept to 5 mm;and rotating the wireless power receiver sequentially by 0°, 90°, 180°,and 270°.

As may be seen from the result of FIG. 15, the Q factor (Q_(RX) @0 mm)measured at the center of the reference wireless power transmitter isdifferent from the Q factor (Q_(RX) @5 mm) measured at the positionseparated by 5 mm from the center. Meanwhile, it may be seen that whenthe thickness of a metal case is increased, both of Q_(RX) @0 mm andQ_(RX) @5 mm are increased.

Considered next is the case where the wireless power receiver is placedon the reference wireless power transmitter; a second Q factor(Q_(RX_RFO)) which is a reference Q factor that may be obtained from thereference wireless power transmitter is derived under a condition that arepresentative foreign object is present in the surroundings thereof.

FIG. 16 is a perspective view of a primary coil and shielding unit of areference wireless power transmitter; a secondary coil, shielding unit,and metal case member of a reference wireless power receiver; andrepresentative foreign objects used for an experiment of the presentembodiment.

The power transmitting unit of a reference wireless power transmitterand a reference wireless power receiver used in the experiment andsimulation of FIG. 16 are the same as the power transmitting unit 1200of FIG. 12 and the wireless power receiver of FIG. 14; and foreignobjects used in the experiments (a), (b), (c), and (d) are the same asthe representative foreign object of FIG. 13, respectively. When asimulation is performed under the condition of FIG. 16, a result asshown in FIGS. 17a to 17d may be obtained.

FIGS. 17a to 17d illustrate a simulation result performed in theenvironment of FIG. 16 according to the present embodiment.

FIG. 17a is a simulation result in the environment of FIG. 16(a), FIG.17b in the environment of FIG. 16(b), FIG. 17c in the environment ofFIG. 16(c), and FIG. 17d in the environment of FIG. 16(d).

A foreign object degrades a Q factor. Therefore, a Q factor measured inthe presence of a foreign object is usually smaller than a reference Qfactor in the absence of a foreign object. Therefore, when a method fordetecting a foreign object based on a Q factor is used, it is determinedthat a foreign object exists when a measured Q factor is smaller than areference Q factor. However, if a measured Q factor is equal to or evengreater than a reference Q factor in spite of the presence of a foreignobject, it may be erroneously judged that a foreign object does notexist. In other words, despite the general observation that when aforeign object is inserted, the Q factor becomes smaller than areference Q factor in the absence of a foreign object due to the losscaused by the foreign object, if a measured Q factor becomes evengreater than or equal to the reference Q factor (namely the amount ofchange ≥0), the foreign object may not be detected.

Therefore, an optimal reference Q factor is designed by using a methodwhich sets a reference Q factor (first Q factor) obtained when anarbitrary wireless power receiver is placed on a reference wirelesspower transmitter in the absence of a foreign object as a variable andmonitors how much a second Q factor measured in the presence of arepresentative foreign object is changed from the first Q factor

In the respective graphs of FIG. 17a to 17 d, x-axis represents a Qfactor (Q_(ref)) or a first Q factor (Q_(RX)) that a wireless powerreceiver reports to a reference wireless power transmitter; and y-axisrepresents the amount of change in the Q factor (ΔQ_(RFO)) whichdescribes how the specific reference Q factor (Q_(ref)) increases ordecreases due to a representative foreign object. Here, the amount ofchange (ΔQ_(RFO)) in the Q factor may be expressed by the followingequation.

ΔQ _(RFO) =Q _(RX+RFO) −Q _(ref)  [Eq. 1]

Referring to Eq. 1, Q_(RX+RFO) is a measured, second Q factor, andQ_(ref) is a first Q factor reported to a reference wirelesstransmitter.

In a section of x-axis where the second Q factor (Q_(RX+RFO)) measuredwhen a representative foreign object is inserted is larger than or equalto the first Q factor (Q_(ref)), a foreign object is undetectable. Asdescribed above, if a section of the first Q factor in which an errormay occur at the time of detecting a foreign object based on the Qfactor is defined as an undetected section, the undetected section maybe found from the simulation result of FIGS. 17a to 17d . In therespective graphs of FIGS. 17a to 17d , the coordinates (a, b) impliesthat a wireless power receiver is placed at the position offset from thecenter of a reference wireless power transmitter by a along the x-axisand by b along the y-axis. Furthermore, the present embodiment definesan undetected section more conservatively with respect to thecoordinates (0, 5) at which a Q factor measurement error is larger.

And if the first Q factor at the boundary between an undetected sectionand detected section is defined as a threshold Q factor (Q_(ref,OX)), ithas been found from the simulation result that the threshold Q factor isdetermined differently for each representative foreign object. In thecase of FIG. 17a where a first representative foreign object (RFO #1) isused, the threshold Q factor has been found to be 21.4; in the case ofFIG. 17b where a second representative foreign object (RFO #2) is used,the threshold Q factor has been found to be 18.5; in the case of FIG.17c where a third representative foreign object (RFO #3) is used, thethreshold Q factor has been found to be 12.2; and in the case of FIG.17d where a fourth representative foreign object (RFO #4) is used, thethreshold Q factor has been found to be 22.2. The threshold Q factor mayalso be called a first Q factor when the first and the second Q factorare the same with each other.

Wireless power receivers having a first Q factor smaller than or equalto the threshold Q factor belong to the undetected section whilewireless power receivers having a first Q factor larger than thethreshold Q factor belong to the detected section. In other words, ifthe first Q factor is smaller than or equal to the threshold Q factor(Q_(ref)≤Q_(ref.0x)), a foreign object is undetectable. On the otherhand, if the first Q factor is larger than the threshold Q factor(Q_(ref)>Q_(ref.0x)), a foreign object may be detectable.

The detected section common to all of the representative foreign objectsis a section where the first Q factor is larger than the threshold Qfactor (=22.2), and in a section of the first Q factor smaller than thethreshold Q factor, a foreign object may or may not be detecteddepending on the type of the representative foreign object. Therefore,the present embodiment derives an optimal threshold Q factor at whichall of foreign objects may be detected as 22.2 and designs an optimalreference Q factor based on the optimal threshold Q factor. In whatfollows, a method for designing an optimal reference Q factor isdisclosed.

According to the WPC specification, the reference Q factor transmittedto a wireless power transmitter by a wireless power receiver has toprovide accuracy at an error level of ±10%. In other words, thereference Q factor (Q_(ref)) obtained at the time of designing ormanufacturing a wireless power receiver has to satisfy the condition0.9×Q′_(ref)≤Q_(ref)≤1.1×Q′_(ref) from a relationship with a Q factor(Q′_(ref)) measured at the time of an actual wireless power chargingservice. In other words, an optimal reference Q factor (Q_(ref_min)) maybe derived within a range in which the aforementioned condition issatisfied. Considering an error, the minimum value of the reference Qfactor (Q_(ref)) is allowed down to 0.9×Q′_(ref).

Therefore, if a foreign object is to be successfully detected at leastfor all of representative foreign objects, the optimal reference Qfactor (Q_(ref_min)) has only to be designed so that an error value(−10%) allowed for a measured Q factor is at least larger than theoptimal threshold Q factor (namely Q_(ref_min)=Q′_(ref), where0.9×Q′_(ref)>22.2). In this case, a design constraint where the optimalreference Q factor (Q_(ref_min)) is larger than 24.666 is derived. Here,since the optimal reference Q factor is the minimum reference Q factorabove which a foreign object may be detected, the optimal reference Qfactor may also be called the minimum reference Q factor. In whatfollows, for the convenience of descriptions, the optimal reference Qfactor will be called the minimum reference Q factor.

According to one embodiment, the minimum reference Q factor(Q_(ref_min)) may be designed to belong to a range from 24 to 26.Following the design, if the reference Q factor of an arbitrary wirelesspower receiver is less than or equal to 24, the arbitrary wireless powerreceiver fails to pass the foreign object detection performance test.

According to another embodiment, the optimal reference Q factor(Q_(ref_min)) may be designed to belong to a range from 24.66 to 25.Following the design, if the reference Q factor of an arbitrary wirelesspower receiver is less than or equal to 24.66, the arbitrary wirelesspower receiver fails to pass the foreign object detection performancetest.

According to yet another embodiment, the optimal reference Q factor(Q_(ref_min)) may be designed to be 24.7. Following the design, if thereference Q factor of an arbitrary wireless power receiver is less thanor equal to 24.7, the arbitrary wireless power receiver fails to passthe foreign object detection performance test. On the other hand, if thereference Q factor of an arbitrary wireless power receiver exceeds 24.7,the arbitrary wireless power receiver passes the foreign objectdetection performance test.

According to still another embodiment, the optimal reference Q factor(Q_(ref_min)) may be designed to be 25. Following the design, if thereference Q factor of an arbitrary wireless power receiver is less thanor equal to 25, the arbitrary wireless power receiver fails to pass theforeign object detection performance test. On the other hand, if thereference Q factor of an arbitrary wireless power receiver exceeds 25,the arbitrary wireless power receiver passes the foreign objectdetection performance test.

FIG. 18 illustrates a flow diagram of a method for receiving wirelesspower from a wireless power transmitter based on foreign objectdetection by a wireless power receiver according to one embodiment ofthe present invention.

Referring to FIG. 18, a wireless power receiver receives digital pingfrom a wireless power transmitter S1800. Afterwards, the wireless powerreceiver transmits an identification and configuration packet to thewireless power transmitter S1805. When the identification andconfiguration packet is transmitted to the wireless power transmitter,the wireless power receiver and the transmitter enter the negotiationphase.

In the negotiation phase, the wireless power receiver transmits aforeign object detection state packet which indicates a reference Qfactor (Q_(ref)) of the wireless power receiver to the wireless powertransmitter S1810.

The wireless power receiver receives wireless power through magneticcoupling from the wireless power transmitter based on the foreign objectdetection result of the wireless power transmitter which uses thereference Q factor S1815. If it is determined that a foreign object hasbeen detected, the wireless power transmitter does not transmit powerbased on an extended power profile. In other words, if a foreign objectis detected, the wireless power transmitter may transmit power based ona basic power profile or stop transmission of power and enter a standbystate. In this case, the wireless power receiver may or may not receivewireless power based on the basic power profile. On the other hand, ifit is determined that a foreign object has not been detected, thewireless power transmitter may transmit wireless power based on theextended power profile, and the wireless power receiver may receiveincreased wireless power from the wireless power transmitter.

Here, the reference Q factor is a Q factor of a reference wireless powertransmitter with respect to the wireless power receiver in the absenceof a nearby foreign object, and the reference Q factor may be largerthan or equal to the minimum reference Q factor (Q_(ref_min)) requiredfor an arbitrary wireless power receiver compatible with the referencewireless power transmitter.

As one example, provided that a first Q factor (Q_(RX)) of a referencewireless power transmitter with respect to the arbitrary wireless powerreceiver in the absence of a nearby foreign object is the same as asecond Q factor (Q_(RX,RFO)) of the reference wireless power transmitterwith respect to the arbitrary wireless power receiver in the presence ofa nearby representative foreign object (RFO), if the first Q factor isdenoted as a threshold Q factor (Q_(ref,OX)) by which the representativeforeign object may be detected, the minimum Q factor value may bedefined based on the threshold Q factor.

Here, the minimum reference Q factor may be defined as a value whichcompensates the threshold Q factor for as much as 10% which is a Qfactor measurement error. In one aspect, the threshold Q factor may be avalue within a range from 22 to 23, the Q factor measurement error maycorrespond to 10% of the threshold Q factor, and the minimum reference Qfactor may be a value within a range from 24 to 26. In another aspect,the threshold Q factor may be a value within a range from 22 to 23, theQ factor measurement error may correspond to 10% of the threshold Qfactor, and the minimum reference Q factor may be a value within a rangefrom 24 to 26. In yet another aspect, the threshold Q factor may be22.2, and the minimum reference Q factor may be a value within a rangefrom 24.7 to 25. Also, the representative foreign object may be a fourthrepresentative foreign object among various types of representativeforeign objects, which maximizes the threshold Q factor.

As another example, when ΔQ factor=second Q factor−first Q factor, theminimum reference Q factor may be defined based on the first Q factorwhich satisfies ΔQ factor=0; the first Q factor may be a Q factor of areference wireless power transmitter with respect to the arbitrarywireless power receiver in the absence of a nearby foreign object; andthe second Q factor may be a Q factor of the reference wireless powertransmitter with respect to the arbitrary wireless power receiver in thepresence of a nearby representative foreign object.

FIG. 19 illustrates a flow diagram of a method for transmitting wirelesspower to a wireless power receiver based on foreign object detection bya wireless power transmitter according to one embodiment of the presentinvention.

Referring to FIG. 19, a wireless power transmitter transmits digitalping to a wireless power receiver S1900.

Afterwards, the wireless power transmitter receives an identificationand configuration packet from a wireless power receiver S1905. When theidentification and configuration packet is received from the wirelesspower receiver, the wireless power receiver and the transmitter enterthe negotiation phase.

In the negotiation phase, the wireless power transmitter receives aforeign object detection state packet which indicates a reference Qfactor (Q_(ref)) of the wireless power receiver from the wireless powerreceiver S1910.

The wireless power transmitter transmits wireless power through magneticcoupling to the wireless power receiver based on the foreign objectdetection result of the wireless power transmitter which uses thereference Q factor S1915. If it is determined that a foreign object hasbeen detected, the wireless power transmitter does not transmit powerbased on an extended power profile. In other words, if a foreign objectis detected, the wireless power transmitter may transmit power based ona basic power profile or stop transmission of power and enter a standbystate. In this case, the wireless power receiver may or may not receivewireless power based on the basic power profile. On the other hand, ifit is determined that a foreign object has not been detected, thewireless power transmitter may transmit wireless power based on theextended power profile, and the wireless power receiver may receiveincreased wireless power from the wireless power transmitter.

Here, the reference Q factor is a Q factor of a reference wireless powertransmitter with respect to the wireless power receiver in the absenceof a nearby foreign object, and the reference Q factor may be largerthan or equal to the minimum reference Q factor (Q_(ref_min)) requiredfor an arbitrary wireless power receiver compatible with the referencewireless power transmitter.

As one example, provided that a first Q factor (Q_(RX)) of a referencewireless power transmitter with respect to the arbitrary wireless powerreceiver in the absence of a nearby foreign object is the same as asecond Q factor (Q_(RX,RFO)) of the reference wireless power transmitterwith respect to the arbitrary wireless power receiver in the presence ofa nearby representative foreign object (RFO), if the first Q factor isdenoted as a threshold Q factor (Q_(ref,OX)) by which the representativeforeign object may be detected, the minimum Q factor value may bedefined based on the threshold Q factor.

Here, the minimum reference Q factor may be defined as a value whichcompensates the threshold Q factor for as much as 10% which is a Qfactor measurement error. In one aspect, the threshold Q factor may be avalue within a range from 22 to 23, the Q factor measurement error maycorrespond to 10% of the threshold Q factor, and the minimum reference Qfactor may be a value within a range from 24 to 26. In another aspect,the threshold Q factor may be a value within a range from 22 to 23, theQ factor measurement error may correspond to 10% of the threshold Qfactor, and the minimum reference Q factor may be a value within a rangefrom 24 to 26. In yet another aspect, the threshold Q factor may be22.2, and the minimum reference Q factor may be a value within a rangefrom 24.7 to 25. Also, the representative foreign object may be a fourthrepresentative foreign object among various types of representativeforeign objects, which maximizes the threshold Q factor.

As another example, when ΔQ factor=second Q factor−first Q factor, theminimum reference Q factor may be defined based on the first Q factorwhich satisfies ΔQ factor=0; the first Q factor may be a Q factor of areference wireless power transmitter with respect to the arbitrarywireless power receiver in the absence of a nearby foreign object; andthe second Q factor may be a Q factor of the reference wireless powertransmitter with respect to the arbitrary wireless power receiver in thepresence of a nearby representative foreign object.

FIG. 20 illustrates a flow diagram of a method for testing foreignobject detection performance of a wireless power receiver in a wirelesspower transfer system according to one embodiment of the presentinvention.

Referring to FIG. 20, a test method according to the present embodimentcomprises measuring a Q factor with respect to a wireless power receiverat a predetermined test position on a reference wireless powertransmitter S2000; comparing the measured Q factor with a reference Qfactor reported by the wireless power receiver through an FOD statepacket S2005; and if the reference Q factor is larger than or equal tothe minimum reference Q factor (Q_(ref_min)) required for an arbitrarywireless power receiver compatible with the reference wireless powertransmitter S2010, and the measured Q factor belongs to an error range(±10%) of the reference Q factor S2015, determining a foreign objectdetection performance test of the wireless power receiver as beingsuccessful S2020.

Meanwhile, in the S2010 step, if the reference Q factor is smaller thanthe minimum reference Q factor, it is determined that the test hasfailed S2025. Also, if the Q factor measured in the S2015 step does notbelong to the error range (10%) with respect to the reference Q factor,it is determined that the test has failed S2025.

FIG. 21 is a block diagram of an FOD state packet according to oneembodiment of the present invention.

Referring to FIG. 21, an FOD state packet may be composed of two bytes(B1, B2), for example. Of the two bytes, the first byte (B1) includes aninformation field (Q_(ref)><Q′_(ref)) showing the result of comparing areference Q factor with the minimum reference Q factor, reserved field,and mode field. The second byte (B2) includes a field indicating thereference Q factor. Although the figure illustrates that the informationfield (Q_(ref)><Q′_(ref)) is composed of two bits and positioned at thefirst byte, the information field may be positioned at the second byteor positioned between the reserved field and mode field or after themode field; and even the number of bits may be 1 bit or 3 bits or morerather than 2 bits.

Meanwhile, the information field (Q_(ref)><Q′_(ref)) may indicate thefollowing as shown in Table 6.

TABLE 6 Q_(ref) >< Q′_(ref) Indication 00 Q_(ref) >< Q′_(ref) 01Reserved 10 Reserved 11 Q_(ref) < Q′_(ref)

Referring to Table 6, if the information field (Q_(ref)><Q′_(ref)) is11, it indicates that a foreign object detection method based on Qfactor is unreliable, and a foreign object detection method such asproviding an alarm by which a user may directly check existence of aforeign object may be invoked.

Since all of the constituting elements or steps pertaining to a wirelesspower transmitter and method for transmitting power wirelessly or awireless power receiver and method for receiving power wirelesslyaccording to an embodiment of the present invention described above arenot essential, the wireless power transmitter and method fortransmitting power wirelessly or the wireless power receiver and methodfor receiving power wirelessly may be performed by using the whole orpart of the constituting elements or steps. Also, embodiments of thewireless power transmitter and method for transmitting power wirelesslyor the wireless power receiver and method for receiving power wirelesslymay be performed in combination with each other. Also, the constitutingelements or steps do not necessarily have to be performed in the orderas described above, and a step which has been described later may beperformed before the steps described earlier.

The description given above is merely an embodiment for illustratingtechnical principles of the present invention, and various changes andmodifications are possible from the disclosure by those skilled in theart to which the present invention belongs without deviating from theinherent characteristics of the present invention. Therefore, theembodiments of the present invention described above may be implementedseparately from each other or in the form of a combination thereof.

Therefore, it should be understood that embodiments disclosed in thepresent specification are not intended to limit the technical principlesof the present invention but to support describing the presentinvention, and thus the technical scope of the present invention is notlimited by the embodiments. The technical scope of the present inventionshould be judged by the appended claims, and all of the technicalprinciples found within the range equivalent to the technical scope ofthe present invention should be interpreted to belong thereto.

Irrespective of individual characteristics of a wireless power receiver,accuracy and reliability of detecting a foreign object may be improved.

What is claimed is:
 1. A method for receiving wireless power from awireless power transmitter by a wireless power receiver based on foreignobject detection in a wireless power transfer system, the methodcomprising: receiving a digital ping from the wireless powertransmitter; transmitting a configuration packet to the wireless powertransmitter; transmitting a foreign object detection status packetincluding a reference Q factor (Q_(ref)) of the wireless power receiverto the wireless power transmitter; and receiving wireless power from thewireless power transmitter based on a result of foreign objectdetection, wherein the foreign object detection is performed by thewireless power transmitter based on the reference Q factor, wherein thereference Q factor is determined based on Q factors obtained at fivepositions, wherein the reference Q factor is larger than or equal to 25.2. The method of claim 1, wherein the reference Q factor is larger thanor equal to 25 which is a minimum Q factor value, wherein a first Qfactor (Q_(RX)) is a property of a reference wireless power transmitterwith respect to the arbitrary wireless power receiver in the absence ofa nearby foreign object, and a second Q factor (Q_(RX,RFO)) is aproperty of the reference wireless power transmitter with respect to thearbitrary wireless power receiver in the presence of a nearbyrepresentative foreign object (RFO), and wherein the minimum Q factor isdefined based on a threshold Q factor which is a value of the first Qfactor in case that the first Q factor has a same value with the secondQ factor.
 3. The method of claim 1, wherein, when ΔQ factor=second Qfactor−first Q factor, a minimum reference Q factor is defined based onthe first Q factor which satisfies ΔQ factor=0; the first Q factor is aQ factor of a reference wireless power transmitter with respect to thearbitrary wireless power receiver in the absence of a nearby foreignobject; and the second Q factor is a Q factor of the reference wirelesspower transmitter with respect to the arbitrary wireless power receiverin the presence of a nearby representative foreign object.
 4. The methodof claim 1, wherein a minimum reference Q factor is defined as a valuecompensating the threshold Q factor for a Q factor measurement error. 5.The method of claim 4, wherein the threshold Q factor ranges from 22 to23, the Q factor measurement error lies within 10% of the threshold Qfactor, and the minimum reference Q factor ranges from 24 to
 26. 6. Themethod of claim 5, wherein the threshold Q factor is 22.2.
 7. The methodof claim 6, wherein the minimum reference Q factor ranges from 24.7 to25.
 8. The method of claim 2, wherein the representative foreign objectis a representative foreign object which maximizes the threshold Qfactor among various types of representative foreign objects.
 9. Amethod for transferring wireless power to a wireless power receiver by awireless power transmitter based on foreign object detection in awireless power transfer system, the method comprising: transmitting adigital ping to the wireless power receiver; receiving a configurationpacket from the wireless power receiver; receiving a foreign objectdetection status packet which informs a reference Q factor (Q_(ref)) ofthe wireless power receiver from the wireless power receiver; performingforeign object detection based on the reference Q factor; andtransferring wireless power to the wireless power receiver based on aresult of the foreign object detection, wherein the reference Q factoris determined based on Q factors obtained at five positions, wherein thereference Q factor is larger than or equal to
 25. 10. The method ofclaim 9, wherein if the first Q factor is denoted as a threshold Qfactor (Q_(ref,OX)) by which the representative foreign object isdetected where a first Q factor (Q_(RX)) of a reference wireless powertransmitter with respect to the arbitrary wireless power receiver in theabsence of a nearby foreign object is the same as a second Q factor(Q_(RX,RFO)) of the reference wireless power transmitter with respect tothe arbitrary wireless power receiver in the presence of a nearbyrepresentative foreign object (RFO), a minimum Q factor value is definedbased on the threshold Q factor.
 11. The method of claim 9, wherein,when ΔQ factor=second Q factor−first Q factor, a minimum reference Qfactor is defined based on the first Q factor which satisfies ΔQfactor=0; the first Q factor is a Q factor of a reference wireless powertransmitter with respect to the arbitrary wireless power receiver in theabsence of a nearby foreign object; and the second Q factor is a Qfactor of the reference wireless power transmitter with respect to thearbitrary wireless power receiver in the presence of a nearbyrepresentative foreign object.
 12. The method of claim 11, wherein theminimum reference Q factor is defined as a value compensating thethreshold Q factor for a Q factor measurement error.
 13. The method ofclaim 12, wherein the threshold Q factor ranges from 22 to 23, the Qfactor measurement error lies within 10% of the threshold Q factor, andthe minimum reference Q factor ranges from 24 to
 26. 14. The method ofclaim 13, wherein the threshold Q factor is 22.2.